A .357 Magnum can safely and readily shoot the following rounds: .38 Short Colt, .38 Long Colt, .38 Special, .357 Magnum. Your big problem in the short-near term is that shooting shorter cases will foul cylinders further back in the chamber and if not cleaned thoroughly after shooting, you may not be able to seat longer rounds from baked on carbon build up. Clean soon as possible and do a good job to prevent it. Additionally, in the long term, over years of shooting shorter cartridges in your .357, you will tend to get erosion further back in the cylinder, much like what happens to muzzle breaks/flash hiders on an AR platform, for example.
Some folks even stuff .38 S&W and .38 S&W Short in older models that will take them, but don't do this--they are a different case diameter and should only be shot in pistols designed for them. If you do, in any case, they usually expand and become a pain to reload. Just don't do this. If for no other reason than if you keep/shoot them in a pistol you're using for self defense, and need to reload, one or more stuck casings means that if you're using a speed loader, you just hit a stoppage point that if you haven't trained to deal with may cost you your life. And even if you have, it may still, because it will take additional time to deal with. Again, stay away from .38 S&W/S&W Short in a .38 SPL or .357 Magnum.
Additionally, if you decide to buy a companion lever action rifle, keep in mind that if you wanted to shoot .38 Special out of them, you should buy one designed to shoot .38 SPL and .357 Mag--some that will chamber and shoot .357 Mag will also chamber and fire a .38 SPL, but will not extract or eject it, and/or they will be problematic cycling .38 SPL rounds.
I've dealt with both the shooting of the smaller rounds (very popular in SA/Cowboy shooting) in .357 Mag pistols, and the .38 SPL chambering, extracting, and ejecting issues in rifles while working in the firearms industry. One additional and nice reason to actually shoot .38 SPL loads in a .357 Mag is the lower recoil and pressures. In fact, it's a popular setup among those who like to carry a snub-nosed revolver, to buy a .357 Mag with the intention of shooting .38 SPL because the .357 Mag is typically made with thicker cylinder walls (and usually frames and barrels) to withstand higher pressures.
This means there's more metal/weight to most .357 Mag snubs than a .38 SPL of a similar barrel length and frame size--which helps offset muzzle rise due to recoil. Thus, time back on target for follow-up shots is quicker. Most recoil sensitive shooters are better off with a semi-auto than a revolver, but if a recoil sensitive shooter wants a snub nosed revolver which is much harder to shoot accurately than just about anything but a derringer, the smart move is to get a Magnum and shoot shorter rounds. You'll find people buy .44 Mag snubs and shoot .44 Special or .44 Russian in them, or they'll buy a .327 Federal Magnum and shoot .32 H&R Magnum or .32 Long Colt.
More weight + less powder = lower felt recoil and faster follow up shots.
As an aside, most often, the above scenario is due to a husband or boyfriend thinking the best handgun for a wife, girlfriend, mother, sister, daughter was a revolver, when it's usually the hardest for them to learn with, shoot accurately, and become comfortable and proficient with simply because the recoil is so unpleasant. Always did everything to steer them away from it when I could, and a great many snub nosed revolvers purchased usually came back within days to be traded on something else, even with reduced recoil loads. Occasionally, it is a guy or gal who knows how to shoot revolvers, and they're looking specifically for the added weight and controllability in a snub nosed pistol.
A final note, you can also shoot .38 SPL+P in your .357 Mag...but you might as well just shoot .357 Mag rounds if you're going to do that. You can even get low recoil/low flash .357 Mag rounds and avoid the chamber fouling/erosion issues that come from prolonged use of .38 SPL or .38 Long Colts. If you reload, just reload them light. The .357 Magnum is incredibly versatile. There are even high pressure .357 Magnum loads using heavier than normal bullets (180 grains as opposed to the more common 158 and 125 grain bullets) which make fantastic hunting rounds.
Check out buffalobore.com for a great example of a variety of high performance and specialty .38 SPL/.357 Mag rounds. Check out buffaloarms.com for a variety of.38 LC, as well as .38 SPL/.357 Mag ammo, including blackpowder rounds.